The present invention belongs to the field of technologies relating to a piezoelectric thin film element that comprises a piezoelectric thin film, first and second electrode films respectively formed on opposite surfaces of the piezoelectric thin film in the thickness direction thereof, and a hold film for holding the piezoelectric thin film, to an ink jet recording head employing such a piezoelectric thin film element, and to their manufacture methods.
Generally, such a type of piezoelectric thin film element has been used as a pyroelectric device for conversion of heat into electric charge or as a piezoelectric device for conversion of mechanical energy into electric energy, and vice versa. Their piezoelectric thin film is usually formed of ferroelectric material such as PZT and PLZT.
The performance of such a piezoelectric thin film element is much influenced by how its piezoelectric thin film is held. For the case of pyroelectric devices, it is required that the piezoelectric thin film be held so that the sensor part decreases in thermal capacity and thermal conductance. On the other hand, for the case of piezoelectric devices, it is required that the piezoelectric thin film be held so that the sensor part undergoes much more deformation by mechanical quantity.
In order to meet the above requirements, Japanese Unexamined Patent Gazette No. H04-170077 proposes a pyroelectric infrared detector (a piezoelectric thin film element) in which a pyroelectric thin film (a piezoelectric thin film) is held by an organic thin film (a hold film) of polyimide resin or the like. In addition to this proposal, there is also proposed a method for the manufacture of such a detector. In accordance with this prior art method, a pyroelectric thin film is formed on a substrate used for film formation. Then, an upper electrode film is formed on the pyroelectric thin film. Following this, an organic thin film is so formed as to cover the pyroelectric thin film. Then, a hold substrate is fixed onto the organic thin film. Thereafter, the film formation substrate is removed by etching. This is followed by formation of an lower electrode film on a surface of the pyroelectric thin film on the side of the film formation substrate before its removal.
However, there is the problem with this prior art proposal. That is, when the film formation substrate is etched away, the pyroelectric thin film is exposed to etchant. As a result, the pyroelectric film damages by etchant. To cope with this drawback, the lower electrode film is, first of all, formed on (or brought into contact with) the film formation substrate and a pyroelectric thin film is then formed on the lower electrode film. As a result of such arrangement, at the time of etching away the film formation substrate, the pyroelectric thin film can be prevented from exposure to etchant because of the presence of the lower electrode film. In this case, generally the lower electrode film and the pyroelectric thin film are set such that their opposing surfaces are substantially the same in size and shape. In addition, the overall circumferences of these opposing surfaces are positioned exactly one upon another and the organic thin film is so formed as to closely adhere to the overall circumference of the lateral surface of each of the lower electrode film and the pyroelectric thin film.
However, the organic thin film, which serves as a hold film of resin material, exhibits poor adhesion to the lower electrode film and to the pyroelectric thin film. As a result, during the etching removal step, there occurs etchant penetration along the interface between the lower electrode film and the hold film. The route, along which the etchant which has penetrated along the interface travels to reach the pyroelectric thin film, is short and straight, so that the etchant will arrive soon at the pyroelectric thin film and finally penetrate along the interface between the pyroelectric thin film and the hold film due to the poor adhesion described above. Accordingly, it is difficult to ensure that the pyroelectric thin film is protected from damage by etchant.
The present invention was made to overcome the above-described disadvantages of the prior art. Accordingly, an object of the present invention is to ensure that the piezoelectric thin film is protected from damage by etchant. More specifically, when fabricating a piezoelectric thin film element, in which a piezoelectric thin film is held by a hold film as described above, by forming on a film formation substrate respective films and thereafter removing the film formation substrate by etching, it is possible to protect, by devising an electrode film that comes into contact with the film formation substrate, the piezoelectric thin film from damage by etchant even when the hold film exhibits poor adhesion to the other films because the hold film comprises resin or the like.
The above-described object of the present invention will be accomplished in the following way. In accordance with the present invention, a first electrode film, which is brought into contact with a film formation substrate, is formed such that the overall circumference of a peripheral edge portion of the first electrode film laterally extends beyond the lateral surface of a piezoelectric thin film and closely adheres to a hold film. Alternatively, a hold film is so formed as to closely adhere, through a protective film, to the overall circumference of the lateral surface of a piezoelectric thin film and the protective film is formed so that the overall circumference of an end portion of the protective film on the side of a first electrode film closely adheres to a peripheral edge portion of the first electrode film.
A first invention is disclosed which is directed to a piezoelectric thin film element. The piezoelectric thin film element of the first invention comprises a piezoelectric thin film, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film. Further, the piezoelectric thin film element is manufactured by forming on a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing a portion of the film formation substrate corresponding to at least the piezoelectric thin film. In the piezoelectric thin film element of the first invention, the first electrode film is formed such that the overall circumference of a peripheral edge portion of the first electrode film extends beyond the lateral surface of the piezoelectric thin film and closely adheres to the hold film.
In the above-described structure, the peripheral edge portion of the first electrode film laterally projects beyond the lateral surface of the piezoelectric thin film. If the projection amount of the peripheral edge portion of the first electrode film is set to an adequate value, this achieves that, even when there occurs etchant penetration along the interface between the peripheral edge portion of the first electrode film and the hold film, the etchant has to take a lengthy and curved route to reach the piezoelectric thin film. That is, on the way to the piezoelectric thin film, the etchant stops penetrating along the interface, so that the etchant will not penetrate deeper toward the piezoelectric thin film. Therefore, even when the hold film is made of, for example, resin material, the piezoelectric thin film can be protected from damage by etchant without fail.
A second invention is disclosed which is directed to a piezoelectric thin film element. The piezoelectric thin film element of the second invention comprises a piezoelectric thin film, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film. Further, the piezoelectric thin film element is manufactured by forming n a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing a portion of the film formation substrate corresponding to at least the piezoelectric thin film. In the piezoelectric thin film element of the second invention, the hold film is so formed as to closely adhere, through a protective film, to the overall circumference of the lateral surface of the piezoelectric thin film and the protective film is formed such that the overall circumference of an end portion of the protective film on the side of the first electrode film closely adheres to a peripheral edge portion of the first electrode film.
As a result of such arrangement, the piezoelectric thin film is covered with the first electrode film and the protective film. It is possible to enhance the adhesion between the first electrode film and the protective film. Therefore, it is possible to prevent etchant from coming into contact with the piezoelectric thin film. On the other hand, even when the adhesion between the protective film and the hold film is poor resulting in etchant penetration along the interface between these films, the etchant has to take a lengthy and curved route to reach the piezoelectric thin film. That is, on the way to the piezoelectric thin film, the etchant stops penetrating along the interface between the protective film and the hold film, so that the etchant will not penetrate deeper toward the piezoelectric thin film. Accordingly, the same operation and effects as the first invention can be obtained.
A third invention is disclosed in which the piezoelectric thin film of each first and second invention is formed of ferroelectric material. As a result of such arrangement, it becomes possible to facilitate obtaining high-performance pyroelectric devices and piezoelectric devices.
A fourth and a fifth invention are disclosed which are directed to their respective ink jet recording heads making utilization of the piezoelectric thin film element of the first invention. The fourth invention is directed to an ink jet recording head comprising:
(a) a piezoelectric thin film element;
the piezoelectric thin film element comprising a piezoelectric thin film formed of ferroelectric material, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film;
the piezoelectric thin film element being manufactured by forming on a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing the entire film formation substrate;
(b) a head body;
the head body being positioned, through a diaphragm film, on a surface of the second electrode film of the piezoelectric thin film element on the side opposite to the piezoelectric thin film;
the head body including a recessed portion which becomes a pressure chamber when blocked by the diaphragm film, an ink supply passage for supplying ink to the pressure chamber, and an ink nozzle in communication with the pressure chamber;
wherein the piezoelectric thin film element is operated by applying voltage to the piezoelectric thin film through the first and second electrode films, thereby applying pressure to the pressure chamber to cause the ink in the pressure chamber to jet from the ink nozzle. In the ink jet recording head of the fourth invention, the first electrode film of the piezoelectric thin film element is formed such that the overall circumference of a peripheral edge portion of the first electrode film extends beyond the lateral surface of the piezoelectric thin of film and closely adheres to the hold film.
On the other hand, the fifth invention is directed to an ink jet recording head comprising:
(a) a piezoelectric thin film element;
the piezoelectric thin film element comprising a piezoelectric thin film formed of ferroelectric material, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film;
the piezoelectric thin film element being manufactured by forming on a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing a portion of the film formation substrate corresponding to the piezoelectric thin film;
(b) a head body;
the head body being positioned on a surface of the film formation substrate of the piezoelectric thin film element on the side opposite to the first electrode film;
the head body including a recessed portion which forms, together with a portion of the film formation substrate resulting from the etching removal, a pressure chamber, an ink supply passage for supplying ink to the pressure chamber, and an ink nozzle in communication with the pressure chamber; and
(c) a diaphragm film which is formed on a surface of the second electrode film of the piezoelectric thin film element on the side opposite to the piezoelectric thin film;
wherein the piezoelectric thin film element is operated by applying voltage to the piezoelectric thin film through the first and second electrode films, thereby applying pressure to the pressure chamber to cause the ink in the pressure chamber to jet from the ink nozzle. In the ink jet recording head of the fifth invention, the first electrode film of the piezoelectric thin film element is formed such that the overall circumference of a peripheral edge portion of the first electrode film extends beyond the lateral surface of the piezoelectric thin film and closely adheres to the hold film.
The fourth and fifth inventions each achieve the same operation and effects that the piezoelectric thin film element of the first invention does. The piezoelectric thin film element of the ink jet recording head of each of the fourth and fifth inventions functions as a piezoelectric actuator by which ink in the pressure chamber is emitted from the ink nozzle. This therefore maintains the ink emission performance of the ink jet recording head at high level.
A sixth and a seventh invention are disclosed which are directed to their respective ink jet recording heads making utilization of the piezoelectric thin film element of the second invention. The sixth invention is directed to an ink jet recording head comprising:
(a) a piezoelectric thin film element;
the piezoelectric thin film element comprising a piezoelectric thin film formed of ferroelectric material, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film;
the piezoelectric thin film element being manufactured by forming on a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing a portion of the film formation substrate corresponding to the piezoelectric thin film;
(b) a head body;
the head body being positioned on a surface of the film formation substrate of the piezoelectric thin film element on the side opposite to the first electrode film;
the head body including a recessed portion which forms, together with a portion of the film formation substrate resulting from the etching removal, a pressure chamber, an ink supply passage for supplying ink to the pressure chamber, and an ink nozzle in communication with the pressure chamber; and
(c) a diaphragm film which is formed on a surface of the second electrode film of the piezoelectric thin film element on the side opposite to the piezoelectric thin film;
wherein the piezoelectric thin film element is operated by applying voltage to the piezoelectric thin film through the first and second electrode films, thereby applying pressure to the pressure chamber to cause the ink in the pressure chamber to jet from the ink nozzle. In the ink jet recording head of the sixth invention, the hold film of the piezoelectric thin film element is so formed as to closely adhere, through a protective film, to the overall circumference of a lateral surface of the piezoelectric thin film and the protective film is formed such that the overall circumference of an end portion of the protective film on the side of the first electrode film closely adheres to the overall circumference of a peripheral edge portion of the first electrode film.
On the other hand, the seventh invention is directed to an ink jet recording head comprising:
(a) a piezoelectric thin film element;
the piezoelectric thin film element comprising a piezoelectric thin film formed of ferroelectric material, a first and a second electrode film which are formed respectively on opposite surfaces of the piezoelectric thin film in the direction of the thickness of the piezoelectric thin film, and a hold film which is so formed as to closely adhere to the overall circumference of a lateral surface of the piezoelectric thin film and which holds the piezoelectric thin film;
the piezoelectric thin film element being manufactured by forming on a film formation substrate all of the films with the first electrode film brought into contact with the film formation substrate and thereafter by removing the entire film formation substrate;
(b) a head body;
the head body being positioned, through a diaphragm film, on a surface of the second electrode film of the piezoelectric thin film element on the side opposite to the piezoelectric thin film;
the head body including a recessed portion which becomes a pressure chamber when blocked by the diaphragm film, an ink supply passage for supplying ink to the pressure chamber, and an ink nozzle in communication with the pressure chamber; wherein the piezoelectric thin film element is operated by applying voltage to the piezoelectric thin film through the first and second electrode films, thereby applying pressure to the pressure chamber to cause the ink in the pressure chamber to jet from the ink nozzle. In the ink jet recording head of the seventh invention, the hold film of the piezoelectric thin film element is so formed as to closely adhere, through a protective film, to the overall circumference of the lateral surface of the piezoelectric thin film and the protective film is formed such that the overall circumference of an end portion of the protective film on the side of the first electrode film closely adheres to the overall circumference of a peripheral edge portion of the first electrode film.
The sixth and seventh inventions each achieve the same operation and effects that the piezoelectric thin film element of the second invention does and it is possible to maintain the ink emission performance of the recording head at high level.
An eighth and a ninth invention are disclosed which are directed to their respective piezoelectric thin film element manufacture methods. The manufacture method of the eighth invention comprises a step of forming a first electrode film on a film formation substrate, a step of forming a piezoelectric thin film on other than the overall circumference of a peripheral edge portion of the first electrode film, a step of forming a hold film all around the piezoelectric thin film over the film formation substrate so that the hold film closely adheres to the overall circumference of a lateral surface of the piezoelectric thin film and to the overall circumference of the peripheral edge portion of the first electrode film, a step of forming a second electrode film on the piezoelectric thin film, and after completion of all of the above steps, a step of removing, by etching, a portion of the film formation substrate corresponding to at least the piezoelectric thin film.
As a result of such arrangement, the first electrode film is formed such that the overall circumference of a peripheral edge portion of the first electrode film projects laterally beyond the lateral surface of the piezoelectric thin film and closely adheres to the hold film. This facilitates formation of the piezoelectric thin film element of the first invention.
On the other hand, the manufacture method of the ninth invention comprises a step of forming a first electrode film on a film formation substrate, a step of forming a piezoelectric thin film on the first electrode film, a step of forming a protective film all around the piezoelectric thin film over the film formation substrate so that the protective film closely adheres to the overall circumference of a lateral surface of the piezoelectric thin film and to the overall circumference of a peripheral edge portion of the first electrode film, a step of forming a hold film all around the protective film over the film formation substrate so that the hold film closely adheres to the protective film, a step of forming a second electrode film on the piezoelectric thin film, and after completion of all of the above steps, a step of removing, by etching, a portion of the film formation substrate corresponding to at least the piezoelectric thin film.
As a result of such arrangement, the hold film is so formed as to closely adhere, through the protective film, to the overall circumference of the lateral surface of the piezoelectric thin film, and the protective film is formed such that the overall circumference of the end portion of the protective film on the side of the first electrode film closely adheres to the peripheral edge portion of the first electrode film. This facilitates formation of the piezoelectric thin film element of the second invention.
A tenth and an eleventh invention are disclosed which are directed to their respective methods for the manufacture of an ink jet recording head comprising a piezoelectric thin film element which undergoes deformation, together with a diaphragm film, by the piezoelectric effect of a piezoelectric thin film formed of ferroelectric material, thereby causing ink in a pressure chamber to jet therefrom. The manufacture method of the tenth invention comprises a step of forming a first electrode film on a film formation substrate, a step of forming the piezoelectric thin film on other than the overall circumference of a peripheral edge portion of the first electrode film, a step of forming a hold film all around the piezoelectric thin film over the film formation substrate so that the hold film closely adheres to the overall circumference of a lateral surface of the piezoelectric thin film and to the overall circumference of the peripheral edge portion of the first electrode film, a step of forming a second electrode film on the piezoelectric thin film, a step of forming the diaphragm film on the second electrode film, a step of fixing the diaphragm film and a head body having a recessed portion which forms, together with the diaphragm film, a pressure chamber, and, upon completion of all of the above steps, a step of removing, by etching, the entire film formation substrate. This facilitates formation of the ink jet recording head of the fourth invention.
The manufacture method of the eleventh invention comprises a step of forming a first electrode film on a film formation substrate, a step of forming the piezoelectric thin film on the first electrode film, a step of forming a protective film all around the piezoelectric thin film over the film formation substrate so that the protective film closely adheres to the overall circumference of a lateral surface of the piezoelectric thin film and to the overall circumference of a peripheral edge portion of the first electrode film, a step of forming a hold film all around the protective film over the film formation substrate so that the hold film closely adheres to the protective film, a step of forming a second electrode film on the piezoelectric thin film, a step of forming the diaphragm film on the second electrode film, upon completion of all of the above steps, a step of removing, by etching, a portion of the film formation substrate corresponding to the piezoelectric thin film, and after the etching removal step, a step of fixing the film formation substrate and a head body having a recessed portion which forms, together with a portion of the film formation substrate resulting from the etching removal, the pressure chamber. This facilitates formation of the ink jet recording head of the sixth invention.